Recently, the performance and functionality of digital cameras and digital movie cameras that use some solid-state image sensor such as a CCD and a CMOS (which will be sometimes simply referred to herein as an “image sensor”) have been enhanced to an astonishing degree. In particular, the size of a pixel structure for use in a solid-state image sensor has been further reduced these days thanks to rapid development of solid-state image sensor processing technologies, thus getting an even greater number of pixels and drivers integrated together in a solid-state image sensor. And the performance of image sensors has been further enhanced as well. Meanwhile, cameras that use a backside illumination type image sensor, which receives incoming light on its reverse side, not on its front side with a wiring layer for the solid-state image sensor, have been developed just recently and their property has attracted a lot of attention these days. An ordinary image sensor receives incoming light on its front side with the wiring layer, and therefore, no small part of the incoming light would be lost due to the presence of a complicated structure on the front side. In the backside illumination type image sensor, on the other hand, nothing in its photodetector section will cut off the incoming light, and therefore, almost no part of the incoming light will be lost by the device structure. Such a backside illumination type solid-state image sensor is disclosed in Patent Document No. 1, for example.
Patent Document No. 2 discloses a technique for making a photoelectric conversion more efficiently at a pixel by providing a reflective film for the sidewall of the photoelectric conversion section of such a backside illumination type image sensor. On the other hand, Patent Document No. 3 discloses a technique for increasing the photoelectric conversion efficiency by providing a reflective layer behind a photosensitive section and by getting incoming light, which has been transmitted through a photoelectric conversion section, reflected by that reflective layer.
As disclosed in Patent Document No. 4, a backside illumination type image sensor may be formed by fabricating a conventional image sensor that receives incoming light on its front side, bonding a substrate to the front side, and then partially removing its reverse side to a level where the photosensitive section can sense the incoming light.